The goal of this Fast Track SBIR is to demonstrate the functionality of PROFUSA's novel injectable tissue oxygen monitors in patients with peripheral arterial disease (PAD) and to determine the its ability to detect restenosis in critical limb ischemia (CLI). PAD is a manifestation of systemic atherosclerosis that affects 10-12 million people in the U.S., with prevalence increasing with age. PAD ranges from mild (accompanied by intermittent claudication or pain with exercise) to severe (accompanied by CLI and gangrene), and is associated with high rates of amputation, mortality and poor quality of life. With the appropriate monitoring and treatment, disease progression can be halted and even reversed, but easy-to-use, accurate monitoring products to indicate when a change in therapy is needed do not exist. PROFUSA's oxygen sensing technology can help salvage limbs from amputation by providing a way to measure real-time tissue oxygen levels in the ischemic limb before, during, and after treatment, thus enabling appropriate therapy to be administered in a timely fashion before advanced symptoms appear. In this Fast Track SBIR, we propose 1) to confirm biocompatibility according to ISO 10993 standards, 2) to enhance user experience for commercialization by minimizing sensor size and 3) to clinically verify the ability of PROFUSA's tissue oxygen sensors to detect restenosis in PAD/CLI patients. In addition to the strong scientific and pre-clinical teams, medical, clinical, regulatory and business personnel will be an integral part of this project to provide early strategy for successful product development. These data will be crucial in advancing PROFUSA towards commercialization and regulatory approvals.